Interesting stuff. The way the anchor failure tests happened with the weight hanging and an anchor suddenly releasing seems a bit cut and dry. I wonder if there would be any difference in the anchor failure tests if you had a falling mass (climber) pull out the anchor via some sort of preplanned weak point so that you get the full dynamic effect of the momentum of the climber and the shock vibrations in the rope..

This is excellent! I hadn't seen it before! Some of the results are predictable, but it's good to see real data!

The loads here seem reasonable for a rescue situation, but, unfortunately, not for most pure rock climbing situations.

Still, it does at least *hint* at the truth of what might happen in a hanging belay off an anchor when one arm blows. And if the loads were those you'd see in a worst-case scenario (which is exactly the one you build your anchor to handle) then you might expect to see loads like those in the study.

The main thing I wish is that they'd included some of the better anchors from the big anchors thread. Things like the CharlesJMM and the Mooselette make the equalette look like a poor first draft (IMO).

The best of the bunch in the thread were a beautiful blend of what the study calls load-sharing and load-distributing, with features of each. Unlike the load-sharing anchors in the study, these anchors had very little extension. The only real question is how well they'd equalize in a drop scenario - an answer that would have been well tested by this study.

They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems. The ideal could never be what they postulated.

I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this:

[image]http://i43.tinypic.com/qoc1o5.jpg[/image]

What are you seeing that I'm missing?

GO

Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting.

They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems. The ideal could never be what they postulated.

I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this:

What are you seeing that I'm missing?

GO

Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting.

That's not necessarily an problem - a standard cordelette will have differing tension in every arm. It simply means that there is uneven stress on the anchor points.

But upon further reflection, there *is* an issue with my diagram above: assuming no friction, the tension in every strand should be equal.

This is now what the forces look like they should be. So they look to me like (friction etc aside) they should be equal on each strand.

They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems. The ideal could never be what they postulated.

I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this:

[image]http://i43.tinypic.com/qoc1o5.jpg[/image]

What are you seeing that I'm missing?

GO

Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting.

That's not necessarily an issue - a standard cordelette will have differing tension in every arm. It simply means that there is uneven stress on the anchor points.

But upon further reflection, there *is* an issue with my diagram above: assuming no friction, the tension in every strand should be equal. Will post another version shortly.

GO

That's what I meant by uneven pulls, differing tension on opposite sides of the cordolette running to an anchor

The way I read it was that they had a sliding x between anchor 1 and 2, a sliding x between anchor 2 and 3, then a sliding x to join the 2 original x's. This would mean that anchor 2 was repesented in both x's and therefore would see twice the load and that would agree with their results.

The way I read it was that they had a sliding x between anchor 1 and 2, a sliding x between anchor 2 and 3, then a sliding x to join the 2 original x's. This would mean that anchor 2 was repesented in both x's and therefore would see twice the load and that would agree with their results.

Are we talking about the same thing here? I see only one sling in this anchor:

The problem here is that the pair of biners at the bottom are not evenly stranded. If you weight the power point it will pull down the right biner (less stranded) while the left biner (more stranded) goes up ... until the power point contacts the right biner at which point I guess it stabilizes (not quite enough coffee).

I'm assuming everything can slide and friction is negligible, which I think is the intent.

Bill L

Edit: I think I pretty much said the same thing as bigjohnnyc. And I'm assuming the power point is on a sliding X. Take that out and I think the stability issue goes away.

GO, are you sure you can really see that poor photograph well enough to draw an accurate diagram? It sure isn't clear to me. While your sketch might be correct I think it's just as easy to see it as two sliding Xs with four strands going to the center anchor.

Now that would require you to believe that they screwed up their calculation of the ideal static loads. But look at the equalette case. They screwed up the ideal values for that one.

GO, are you sure you can really see that poor photograph well enough to draw an accurate diagram? It sure isn't clear to me. While your sketch might be correct I think it's just as easy to see it as two sliding Xs with four strands going to the center anchor.

You're right, it is a poor photo. But if you think you see four strands going to the middle of the three anchors, you need your eyes examined!

Without wanting to sound too unscientific, what are the conclusions of the more gear-headed people here? I hate using webbing to start with as anchors and will generally use lengths of static rope with appropriate knots etc. I have money, and will pay for my life to be secure up to ~30kn. And wear a helmet. Yes, I'm that uncool.

GO, I see what you're talking about and it is suggestive. But I don't think this photo is good enough to really say one way or the other. It's just too easy to see things in a lousy photo, especially if you're already thinking it's supposed to be there.

Let's take another tack. If you're interpretation is correct the force on each anchor should be the same ideally. The angle between the left and right anchors looks like about 85 degrees or so. For the 595 lb load that would give a value of 240 lbs on each anchor.

If instead four strands go to the center, the ideal would be 171 lbs for the side anchors and 342 lbs for the center one.

ptlong, I'm open to other interpretations of the pic, because, as you said, the detail in the pic is poor. But the photo is far from uninterpretable. Sure, it is difficult to tell where the strands are going as they get to the two power-point biners, so I'm open to other interpretations. But beyond that, you can easily see every strand, and there are not four strands going to the middle anchor.

If you want to make an argument about how either the binding or the large angle could result in the data shown in the article, or if you see the configuration of the sling more clearly than I, in a way that's more consistent with the test results, I'm all ears. But just to say that the data from the forces prove configuration "X" does not make "X" so, when the other data (the photo) clearly invalidates "X" as an answer.

I suppose you could also argue that the pic displayed with that set of data was not actually the anchor configuration tested. That would be a serious allegation against the authors of the article, but at least it would be consistent with the data.